#include <iostream>
#include <cmath>

using namespace std;

double lagrangeInterp(double x[], double y[], int n, double x0) {
    double sum = 0, mult;

    for (int i = 0; i < n; i++) {
        mult = 1;

        for (int j = 0; j < n; j++)
            if (i != j)
                mult *= (x0 - x[j]) / (x[i] - x[j]);
        sum += mult * y[i];
    }

    return sum;
}

int main() {

    const int n = 5;
    double x0;

    double x[n]  {0, 1, 2, 3, 4};
    double y[n]  {1, -1, 0, 10, 35};

    cout << "Enter x: ";
    cin >> x0;

    cout << "f(" << x0 << ") = " << lagrangeInterp(x, y, n, x0) << endl;

    return 0;
}